The problem of dry, damaged skin is well known. The distant ancestors of the human species, upon leaving the ocean, initially adapted to life in a relatively more desiccating terrestrial environment by developing hair-bearing pelts on their bodies. Since then, as evolution forced the erect walk, our ancestors have gradually lost their pelts, developing instead sebum, which makes hair repellent to water and provides hair with tocopherol as an antioxidant. With the industrial revolution, soap and synthetic surfactants have been created and used for washing the skin, with the result that the sebum layer is removed and the skin is left relatively unprotected. For example, the most exposed part of the body now typically is the dorsum of the hands, since people typically wash their hands several times each day, thus eliminating protection by sebum. Moreover, since life expectancy has been increasing, aged people have been showing increased skin damage caused mainly by UV radiation. In addition, dermal fiber proteins and extracellular matrices are crucial for retention of the protective properties of skin. The alteration of the proteins and matrices during actinic aging decreases the resilience of the skin and all other connective tissues, causing changes such as wrinkles. With age, the production of epidermal lipids decreases, resulting in increased trans-epidermal water loss and more dry skin. Thus, the main environmental threats to the skin are penetration of stripping agents such as synthetic detergents, UV radiation, and increased epidermal water loss, especially when the surrounding air is dry and/or cold.
Ideally, a skin-protecting ointment composition should help to solve these problems. Furthermore, the tolerability and sensorial properties of an ointment composition's components must be of a high order, since dry skin is a chronic problem for many people, essentially necessitating application for life.
One approach to solving the problem of dry, damaged skin has been use and application of petrolatum as a major component of skin-protecting ointment compositions. Petrolatum has very desirable characteristics in terms of being long-lasting and water repellant, and, indeed, petrolatum is the standard reference substance for skin protection. However, petrolatum's greasiness and tacky sensory properties are poorly acceptable. An example of greasiness is when a material, often a wholly or partially water immiscible lipid, sticks to the substrate, e.g. skin, with which it is in contact. One problem with a greasy material is that it remains poorly or incompletely absorbed and thus leaves a residue that imparts a tacky, often “lipoidal-like,” sensation upon touch. The sensation is often also described as “greasy.” A related problem with greasy materials is that they readily transfer to substrates that they contact, often contaminating and staining the substrates. Common greasy materials include many fractions of petroleum and related hydrocarbons such as mineral oils, petrolatum, and hydrocarbon/mineral waxes, such as ozokerite; animal fats, such as the lanolins; plant lipids; and synthetic materials, such as many types of silicones, hydrocarbons, esters, ethers, and other structures.
One approach to reduce the greasiness of greasy materials has involved isolation of the materials from substrates, either by encapsulation or by incorporation into the internal, discontinuous phases of emulsions, such as in oil-in-water emulsions. Unfortunately, the amount of greasy materials must be reduced to much less than 50% of their normal amounts in ointment compositions. Since the greasy materials are inside capsules or are in the internal phase of emulsions, the materials do not directly contact the skin or other substrate to which they are applied. Rather, the greasy materials contact the skin or other substrate in a discontinuous mode, thus reducing total contact area and total concentration of greasy materials that can be applied.
Another approach has involved adsorption or absorption of greasy materials onto or into solid components, such as silicates. This approach can be effective. Unfortunately, though, a high amount of adsorbent or absorbent is often required, representing for example 25% to 100% of the weight of the greasy material. The result, again, is a significant reduction in the availability or bioavailability of the greasy material to the substrate.
Accordingly, one object of the present invention is to improve the sensory properties of greasy materials, such as petrolatum, in skin-protecting ointment compositions, since sensory properties are important to acceptance and continued use of the compositions. Another object of the present invention is to accomplish the improvement by adding only a minimal number of safe, well tolerated agents. And another object of the present invention is to enhance inherent UV-protecting properties of greasy materials, again such as petrolatum, in skin-protecting ointment compositions.